This invention relates to fuelling of engines by injection of fuel-gas mixtures to combustion chambers of the internal combustion engines typically operating on either the two or four stroke cycle.
The advantages in terms of low emissions in exhaust gases from internal combustion engines having combustion chambers or cylinders directly injected with fuel-gas mixtures are recognised and result from better control over fuel distributions and quantities than are possible in carburetted engines, in addition to other factors.
In this respect, it has been disclosed by the Applicant in, for example, U.S. Pat. No. 4,800,862 that, in efforts to control the harmful components in the exhaust gases from engines, control of the fuel distribution in the combustion chamber(s) of the engine may be beneficial. Accordingly, that patent discloses, in particular regard to a dual fluid fuel injection system wherein a gas under pressure is used to entrain and deliver a separately metered quantity of fuel to an engine, control over the introduction of fuel to the gas to obtain a predetermined fuel distribution in the combustion chamber(s) of the engine at the time of ignition. In particular, it is described as most desirable in a spark ignition engine that the predetermined fuel distribution involve a relatively fuel rich mixture in proximity to the ignition means at the time of ignition.
Typically, the ignition means is located in the cylinder head of the engine and accordingly, at ignition, a fuel rich region is desirably formed in this area of the cylinder. In certain engines, typically those having centrally mounted direct injection systems, this is accompanied by an adjacent increase in the air/fuel ratio of the remaining combustion charge in the axial direction of the cylinder (ie. becomes leaner). Such a combustion charge is said to be of stratified type and has recognised advantages at ignition, particularly under low load conditions. Low load conditions may be generally described as a load less than 25% of the maximum load achievable at a particular engine speed.
Typically, the preferred fuel distribution in the cylinder will vary with the engine load and speed and so, as described in the Applicant""s U.S. Pat. No. 4,800,862, the rate of introduction of the determined quantities of fuel to the cylinder(s) of the engine is controlled to achieve the most efficient distribution for particular engine operating conditions. Therefore, at high loads it is often more important to have a substantially uniform air/fuel ratio throughout the cylinder such that the fuel is exposed to sufficient air to combust all of the fuel resident within the cylinder. High load may generally be defined as load greater than 75% of the maximum load achievable at a particular engine speed.
It is an object of the present invention to provide a method of fuelling an internal combustion engine which enables efficient operation of the engine with In acceptably low emissions of NOx, hydrocarbons and other pollutants associated with inefficient engine operation.
With this object in view, the present invention provides a method of fuelling an internal combustion engine by injection of a fuelxe2x80x94gas mixture to a combustion chamber of the engine comprising delivering a metered quantity of fuel from a fuel metering means to a delivery injector, the delivery injector being in communication with both the combustion chamber and a supply of pressurised gas for effecting delivery of the metered quantity of fuel to the combustion chamber, wherein at least one of the fuel metering means and the delivery injector are controlled in multiple events and a predetermined fuel distribution is obtained in the combustion chamber at ignition.
The multiple events may occur during a cycle of engine operation to obtain a predetermined fuel distribution in the combustion chamber at ignition during that cycle of engine operation. The fuel metering means may be controlled to effect a single pulse of controlled duration for providing a metered quantity of fuel to the delivery injector. Such a pulse or controlled opening of the fuel metering means may be described as a xe2x80x9cfuel metering eventxe2x80x9d.
The metered quantity of fuel is then delivered entrained in pressurised gas to the combustion chamber by opening of the delivery injector, wherein such a pulse or opening of the delivery injector may be described as a xe2x80x9cgas supply eventxe2x80x9d. The delivery injector may desirably be controlled to effect a plurality of gas supply events which carry fuel directly into the cylinder or combustion chamber of the engine. The delivery injector may be controlled to effect a plurality of pulses of controlled duration during a single cylinder cycle to deliver the metered quantity of fuel to the engine and to, on occasion, enable a desired engine control strategy to be effected. A cylinder cycle may be defined by that period of piston reciprocation between top dead centre and subsequent return to top dead centre. More compendiously, a cylinder cycle may be measured by that period between the piston having any position in the cylinder and subsequent return to that position. Thus, a repeatable sequence of events may occur over a number of cylinder cycles. The sequence of fuel metering and gas supply events is typically contoured over the 360xc2x0 or 720xc2x0 period, depending on whether the engine is to operate on the two or four stroke cycle. Thus, where some of the events in a sequence occur after top dead centre they may be considered to occur during the same cylinder cycle as an earlier such metering or gas supply event that occurred before top dead centre.
The fuel metering means is conveniently in the form of a fuel metering injector and supply of pressurised gas to the delivery injector is typically via a duct or passage communicating the supply of pressurised gas, typically an air compressor, with a holding chamber of the delivery injector. The holding chamber may remain pressurised at all times during engine operation and is preferably selectively communicated directly with the combustion chamber during the plurality of gas or air supply events each cylinder cycle.
In this respect, the method of the present invention may be implemented in a number of ways with the timings of opening/closing of the fuel metering and fuel delivery injectors, otherwise described respectively as the fuel metering and gas supply events, being controllably timed relative to ignition timing, and each other, by the control unit for the engine, typically an electronic control unit. The timing and/or duration of the fuel metering and/or gas supply events may be made a function of engine speed or engine load or both. Further, the fuel metering and gas supply events may in certain applications be overlapped.
While any number of gas or air supply events in the cylinder cycle could be arranged in excess of one, a typical number would be two per cycle. The metered quantity of fuel may be delivered to the delivery injector by the fuel metering means in a fuel metering event timed at any time in the cylinder cycle relative to the gas supply events. For example, initiation of a first gas supply event may enable delivery to the combustion chamber of a portion, desirably a major proportion, of a metered fuel requirement for the engine per cylinder cycle under particular engine operating conditions. Some time later, but during the same cylinder cycle, a second gas or air supply event may deliver any remaining portion of the previously metered fuel amount to the combustion chamber. In some situations, this second air supply event may be initiated to scavenge any xe2x80x9chang-upxe2x80x9d fuel remaining within the fuel delivery injector. It may be initiated either in association with an ignition event or not as desired. That is, a typical delivery injector has a holding chamber or bore through which fuel passes or is retained. A film of fuel may adhere to the walls of the chamber or bore following the first air event due to surface tension effects and it is this phenomenon that is referred to as fuel xe2x80x9chang-upxe2x80x9d or xe2x80x9chang-upxe2x80x9d fuel.
The proportion of fuel delivered to the combustion chamber in the first and subsequent gas supply events may be controlled by varying the timing, duration and/or delivery pressure of each gas supply event. The gas supply events then may be used to achieve splitting of the metered quantity of fuel into discrete pulses of known characteristics which facilitate efficient engine operation by ultimately achieving a predetermined fuel distribution in the combustion chamber at the point of ignition under any given engine operating conditions. Thus, for example, the amount of fuel delivered to the combustion chamber as a result of the first gas supply event may be determined so as to achieve a generally homogeneous mixture throughout the combustion chamber, but one that is not necessarily easily ignitable. Then, just prior to the point of ignition, a second gas supply event may occur in the same operating or cylinder cycle enabling delivery of a sufficient fuel quantity to specifically attain a desired ignitable air/fuel ratio at the ignition means. Such an air/fuel ratio is one recognised by one skilled in this art as being one within the ignitable range. Control of fuelling to the engine in this way is highly conducive to low emission stable engine operation.
As mentioned hereinbefore, the actual quantities of fuel delivered during the separate air supply events is a function of the timing of opening, duration, and/or delivery pressure associated with each air supply event. Accordingly, for the above example, the delivery injector would typically be held open for a longer period for the first air supply event as compared to the second air supply event. This would, of course, depend on the differential pressure drop across the delivery injector when opened, but would be true for a majority of cases.
Alternatively, it may be more beneficial in certain applications or implementations that the amount of fuel delivered to the engine during the first and second gas supply events be not too dissimilar. That is, the amount of fuel in delivered in each gas supply event may be approximately equal. Accordingly, the separate gas supply events may preferably be of similar durations to promote delivery of similar quantities of fuel entrained in air into the combustion chamber of the engine.
In an extension to this concept, all of the metered quantity of fuel may be delivered by the delivery injector during one of the multiple gas supply events to establish the pre-determined fuel distribution in the combustion chamber at ignition. The other gas supply event(s) may then be used to effect other desirable control strategies as will be discussed hereinafter. This is also applicable wherein fuel is supplied to the delivery injector in a plurality of fuel metering events as will also be discussed hereafter. Still further, the other control strategies referred to may, in certain applications, be effected during one of a number of gas supply events even when the gas supply event within a cylinder cycle is being used to deliver a quantity of fuel to the combustion chamber.
For example, in the case where two gas supply events are being affected per cylinder cycle, the subsequent gas supply event may occur late enough in the engine operating cycle such that, subsequent to effecting fuel delivery, the delivery injector may be retained open at a time when the cylinder pressure exceeds that in the chamber or bore of the delivery injector. Thus cylinder gases may be captured and utilised as a source of pressurised gas for subsequent gas supply events in a manner similar to that described in the Applicant""s U.S. Pat. No. 4,936,279, the contents of which are hereby incorporated herein by reference.
Alternatively, the subsequent gas supply event may be used solely for this desired function with all of the metered quantity of fuel being delivered by the delivery injector during the first gas supply event. Hence this methodology may be used to accelerate pressurisation of an air rail on start-up for example or to reduce the air compressor load on the engine at other times. Further, because the bulk or all of the fuel has already been delivered to the engine during the first gas supply event, this gas capture function may be affected at timings and under engine operating conditions which would normally not be conducive to this function.
Still further, any subsequent gas supply event may also be used to affect injector cleaning, as is described in the Applicant""s U.S. Pat. No. 5,195,482, the contents of which are herein incorporated herein by reference. That is, the subsequent gas supply event may, as per the previous gas capture concept, be affected late enough in the engine operating cycle such that the typically high temperature cylinder gases, which are caused to flow into the bore of the delivery injector, may be used to clean the surfaces of the delivery injector subject to carbon deposition (which may adversely affect the fuel delivery accuracy of the delivery injector) in a xe2x80x9cclean routinexe2x80x9d. Thus, admission of cylinder gases to the delivery injector may cause combustion of undesirable carbon deposits and cleaning of the injector surfaces. As per the previous gas capture concept, use of the dual injection concept according to the present invention enables such a clean routine to be effected at timings and under engine operating conditions which normally would not be conducive to such a function. In particular, such an injector cleaning strategy may be effected at any point throughout the load and speed range of the engine as the operation of the engine can be maintained or adjusted as required by way of the fuel delivered to the engine during the first gas or air supply event.
In yet a further extension to this concept, the subsequent gas supply event may be used as a means for enabling provision of increased quantities of fuel to the engine in order to assist with rapid warming of an exhaust system catalyst. One such catalyst warming or xe2x80x9cfast light-offxe2x80x9d strategy is described in the Applicant""s U.S. Pat. No. 5,655,365, the contents of which are hereby incorporated herein by reference. By way of the second or latter gas supply event in a dual injection strategy according to the present invention, late injection of additional fuel into the combustion chamber can be used to provide increased levels of heat energy to any downstream catalyst in the engine exhaust system instead of, or additionally to, the strategy of U.S. Pat. No. 5,655,365. Such fuel may be combusted in the combustion chamber and/or the exhaust system due to the timing of delivery thereof into the combustion chamber with respect to previous ignition event. Again, the use of the dual injection concept according to the present invention enables such a fast light-off strategy to be effected a, timings which would not normally be conducive to such a function and in a manner which may have less of an effect on normal engine running. Further exhaust gas temperature may be maintained above light off under light load running conditions.
In an alternative implementation of the dual injection concept according to the present invention, the fuel metering injector may be controlled to effect a plurality of, typically two, fuel metering events whilst the fuel delivery injector is also controlled to effect a plurality of, typically two, fuel delivery pulses or gas supply events. That is, a first quantity of fuel is metered into the delivery injector early in the cylinder cycle and this metered quantity of fuel is then delivered to the engine early in the cylinder cycle. This first quantity of fuel typically serves to create a homogeneous mixture in the combustion chamber of the engine. A second, generally comparatively much smaller, quantity of fuel is subsequently metered into the delivery injector and this is then delivered to the combustion chamber by way of a second gas supply event. This second gas supply event is generally timed much later in the cylinder cycle so as to provide a rich ignitable mixture around the ignition means just prior to, or at, ignition.
Hence, in this way, a similar desirable fuel distribution is achieved in the combustion chamber, as described hereinabove, by way of two separate fuel metering events and two separate gas supply events. It will be understood that the proportion of fuel metered in each fuel metering event can be varied, as may the proportion of injected air by varying fuel metering injector and delivery injector pulse widths or opening durations respectively. Again, it may be more beneficial in certain applications or implementations that the amount of fuel delivered to the delivery injector during the first and second fuel metering events be not too dissimilar. That is, the amount of fuel delivered in each fuel metering event may be approximately equal. Accordingly, the separate fuel metering events may preferably be of similar durations to promote delivery of similar quantities of fuel to the delivery injector.
Further, such a combination of fuel metering and gas supply events may also be used to effect the other desirable control strategies as previously discussed. That is, whether a latter gas supply event is used to deliver a quantity of fuel to the combustion chamber, or whether all of the fuel is delivered during an earlier gas supply event in the same cylinder cycle, the latter gas supply event may in certain circumstances be used to effect strategies such as cylinder pressure entrapment, injector cleaning and fast catalyst light-off as alluded to hereinbefore.
In yet a further alternative implementation of the dual injection concept according to the present invention, a desirable fuel distribution in the combustion chamber may be achieved by way of two fuel metering events and a single gas supply event. In such a scenario, a first fuel metering event may deliver the bulk of the fuel to be metered to the delivery injector which is subsequently opened to deliver all of this fuel quantity to the engine. However, rather than close the delivery injector once all of this fuel has been delivered, the delivery injector may be held open to deliver a second, smaller quantity of fuel which is subsequently metered into the delivery injector by way of a second, short fuel metering event. Once this second quantity of fuel has been delivered to the combustion chamber in a gas supply event, the delivery injector may be closed, hence having been opened for a single gas supply event only. Such an implementation also provides greater fuel-fluxing control as discussed further in the Applicant""s U.S. Pat. No. 4,800,862, the contents of which are herein incorporated by reference.
Further, it may be possible in some applications, for an air rail pressurisation (xe2x80x9cpump upxe2x80x9d strategy) or delivery injector clean type control strategy to be effected by maintaining the delivery injector open after fuel delivery to the combustion chamber has been completed.
Common to each of the prior discussed implementations of the dual injection concept according to the present invention is the way in which a dual fluid fuel injection system is conveniently used to provide a desirable fuel distribution within the combustion chamber of the engine. That is, the dual fluid fuel injection system is preferably controlled in such a manner so as to deliver the bulk of a metered quantity of fuel into the combustion chamber at a point relatively early in the engine operating cycle, and subsequently controlled to deliver a remainder of the metered quantity of fuel at a point much later in the engine operating cycle.
Preferably, the dual fluid fuel injection system is controlled to provide a generally homogeneous mixture in the combustion chamber at a point relatively early in the engine cylinder cycle.
Preferably, the dual fluid injection system is controlled to provide a small, rich ignitable mixture around the ignition means at a point relatively late in the engine cylinder cycle and generally proximate, that is, just prior, to the timing of ignition.
In contrast to the dissimilar fuel quantities delivered to the engine in accordance with the above methodology, these alternative implementations of the dual injection strategy according to the present invention may equally be adapted to deliver separate, yet similar quantities of fuel to the engine as alluded to hereinbefore. That is, rather than a first gas supply event delivering the bulk of a metered quantity of fuel to the engine and a second gas supply event delivering a smaller quantity of fuel thereto, the separate events may deliver equal or other suitable ratios of fuel to the combustion chamber of the engine. Further, these alternate implementations of the dual injection strategy according to the present invention may be used so as to affect other desirable control strategies whilst still enabling a predetermined fuel distribution to be established in the combustion chamber(s) of the engine prior to ignition. In some cases where a second gas supply event is used solely to affect a desired engine control strategy, the predetermined fuel distribution in the combustion chamber will be established by means of the first gas supply event.
The method according to the present invention may readily be implemented in multi-cylinder engines of both two or four stroke type. The method has particular applicability to four stroke engines as the nature of operation of such engines provides for comparatively longer engine cylinder cycle times within which multiple fuel metering and/or gas supply events may be effected.